Superconductivity of Ce-based heavy fermions under pressure: Valence fluctuation mediated pairing associated with valence instability of Ce

摘要

It is argued that the coincidence of peaks of the residual resistivity and the superconducting transition temperature observed in CeCu_2Ge_2 under pressure can be understood as a phenomenon of enhanced valence fluctuations associated with rapid valence change which is signaled by rapid decrease of the coefficient A of T~2-term of the resistivity. A type of Cooper pairing predicted by this scenario can be different from that mediated by the antiferromagnetic spin fluctuations. The superconductivity observed in isostructural compounds, CeCu_2Si_2 and CeNi_2Ge_2, under pressure should be understood in parallel.